Earlier quoted context omitted.
The right response to this problem - for gmail users - would be to switch to a different email provider. After all, if you are not receiving important mails because Google decides to block them for inexplicable reasons, you are getting an inferior, faulty service. (For me gmail is inferior regardless as my privacy is violated)
Can you suggest free email provider with similar level of service which allows to use your own domain?
They removed the free GSuite tier a long time ago, and they've obscured some the options you could use to configure a similar setup in gmail. I'm not sure if it's still possible.